Study On The Performance And Mechanism Of Defect-rich Heteroatom-doped Carbon-based Materials Activating Persulfate To Degrade Bisphenol A

The persulfate-based advanced oxidation processes（PS-AOPs）have garnered significant interest owing to their exceptional catalytic activity,selectivity,and efficacy in eliminating waterborne persistent organic pollutant.The carbonaceous material as activator of persulfate has garnered significant interest due to its exceptional stability,no secondary pollution caused by metal dissolution and sustainable use.The existing literature shows that construction engineering of heteroatom doping defects（incorporation of non-metallic heteroatoms（N,P,S,etc.）with different electronegativity into the carbon skeleton）is one of the effective strategies to improve carbon materials’performance of promoting PMS activation.The heteroatom doping process can simultaneously endow carbon materials with abundant heteroatom doping defects and intrinsic defects（edge,vacancy,hole or topological defects）.Heteroatom doping defects can break the periodicity of the original carbon structure and optimize the electronic structure and local charge density of the carbon material.Intrinsic defects can provide coordination unsaturated carbon sites with partially localized electrons to regulate redox reactions.However,the activation mechanism of PMS by heteroatom doping defects sites in heteroatom-doped carbon catalysts has usually been focused on,the contribution of intrinsic defects to activate PMS is ignored.Therefore,this study designed and constructed N-doped carbon,N,P co-doped carbon and N,S co-doped carbon.The structure-activity relationship between the active site（intrinsic defect and heteroatom doping defect）and catalytic performance was explored by studying the performance of PMS activation via carbonaceous materials for degradation of emerging pollutants（bisphenol A,BPA）.The results were further extended to the study on the construction and properties of N,P co-doped pomelo peel derived carbon materials,in order to provide a basis for the preparation of biomass carbon materials with high PMS activation performance.The details are as follows:（1）Enhanced peroxymonosulfate activation via 2D N-doped carbon nanosheets for BPA degradation.We synthesized N-rich carbon nanosheets（NCs）through pyrolysis of a glutamic acid and melamine mixture.The contents of pyridine N,pyrrole N and intrinsic defects in NCs increased with the increase of melamine addition,while the content of graphite N decreased.The NC with high N content（17.9 N-atom%,0.15 g/L）showed excellent performance of activating PMS（0.4 mM）to degrade BPA(k=0.127min^-1),and the degradation process of BPA went through three possible pathways,and the environmental risk of intermediate products was gradually reduced.Correlation analysis of each defect site with the first order kinetic constant（k）of the reaction,quenching experiment and electron paramagnetic resonance spectra（EPR）suggest pyridinic and pyrrolic N,rather than graphitic N and intrinsic defects,enhance PMS activation to generate reactive oxygen species(specifically O₂^·-and ¹O₂)and oxidize BPA.Excess halide anions led to significantly increased k with only a limited formation of trichloromethane（disinfection byproducts）（202.76μg/L）in presence of 100 mM Cl^-.（2）Enhanced peroxymonosulfate activation via N,P co-doped carbon microspheres for BPA degradation.We synthesized nitrogen（N）and phosphorus（P）co-doped carbon microspheres（NPCs）through the pyrolysis of aminophosphonic acid resin（D418）precursors.During the programmed temperature rise process,the intrinsic defects are increased with the continuous release of thermally unstable N/P heteroatoms.NPC-1000（pyrolysis temperature at 1000 ^oC,0.15 g/L）with the lowest N and P doping defects and the highest intrinsic defect intensity exhibited excellent performance of activating PMS（1 mM）to degrade BPA(k=0.120 min^-1).Density functional theory（DFT）calculations and correlation analysis between defect sites and k suggest that the adsorption of PMS was facilitated by graphitic N and intrinsic defect sites rather than P doping defect sites,resulting in the degradation of BPA through electron transfer and radical mechanisms,specifically superoxide radicals(O₂^·-).And three possible degradation pathways of BPA were proposed,all the intermediates are transformed into“mutagenicity negative”,reducing environmental risks.Excess halide anions led a significant increase of k with only a limited formation of trichloromethane（TCM）（139.44μg/L）in presence of 100 mM Cl^-.（3）Enhanced peroxymonosulfate activation via N,S co-doped 3D porous carbon for BPA degradation.The N,S co-doped 3D interconnected porous spongy carbon（NSC）was successfully prepared by pyrolysis of the melamine sponge template coated with a mercaptoethylamine-modified polydopamine(PDA film.NSC（0.04 g/L）prepared under optimal conditions exhibits efficient activation of PMS（1 mM）to degrade BPA(k=0.048 min^-1),and the degradation rate of BPA is 1.4 times that of NC.Relevant analysises have shown that intrinsic defects,graphite N and thiophenic S atom doping defects are the main catalytic active sites,and the free radical mechanism dominated by superoxide radicals(O₂^·-)and the non-free radical mechanism dominated by electron transfer are verified.Excess halide anions led a significant increase of k with only a limited formation of trichloromethane（TCM）（169.42μg/L）in presence of 100 mM Cl^-.And the preparation method of the catalyst is a universal method,which is also suitable for shaddock peel template.The BPA degradation rate of N,S co-doped carbon materials(NPC_SP)with pomelo peel（SP）as a template is 3.3 times that of N,S undoped carbon materials(C_SP).（4）Enhanced peroxymonosulfate activation via N,P co-doped biomass-derived carbon nanospheres for BPA degradation.N,P co-doped carbon spheres(NPC_SP)were prepared from grapefruit peel coated with dopamine（DA）and phytic acid（PA）and further carbonized.NPC_SP（0.3 g/L）prepared under optimal conditions exhibits efficient activation of PMS（1 mM）to degrade BPA(k=0.156 min^-1),and the degradation rate of BPA is 2.1 times that of carbon without N,P doping.It has been shown that graphite N,pyrrole N and P atom doping defects are the main activation sites of PMS.At the same time,the synergy of intrinsic defects promotes the catalytic mechanism dominated by O₂^·-.Excess halogen anions(Cl^-,Br^-,and I^-can accelerate the reaction rate（k increases significantly）.In addition,NPC_SP has a wide pH working range and strong anti-ion interference performance,which is conducive to practical water application.In this study,N-doped carbon,N,P co-doped carbon and N,S co-doped carbon were prepared by construction engineering of heteroatom doping defects.By studying the performance of three materials to activate PMS for BPA degradation,the contribution and mechanism of intrinsic defects and heteroatom doping defects were clarified.On this basis,the prepared N,P co-doped pomelo peel biochar also showed good performance in activating PMS to degrade BPA.This study provides basic insights for the identification of active sites in non-metallic heteroatom-doped carbon materials,and also provides a basis for the preparation of highly catalytic active carbon materials.